"I once planned a column about Spencer-Brown, but Donald Knuth talked me
out of it on the grounds that it would give valuable publicity to a
charlatan! But I have some paragraphs about Brown and his flawed
four-color proof, and his Laws of Form, coming up in my Feb column.
Conway once described the book as beautifully written but "content
free." I describe it as a "construction of the propositional calculus in
eccentric notation." But it has a big cult following, and even a
periodical devoted to it."